1. Field of the Invention
This invention generally relates to integrated circuit (IC) fabrication and, more particularly, to a grayscale mask comprised of multiple semi-transparent film layers, and to an associated mask fabrication process.
2. Description of the Related Art
Grayscale masks or reticles are used to expose light-sensitive photoresist (PR) or resin materials. Based upon light exposure, PR films can be formed as temporary masks for the purpose of selectively etching IC films, or for directly patterning the desired shape into a resin. Grayscale and PR masks have application in the fabrication of image sensors, displays, microelectromechanical systems (MEMS), and optical devices to name a few. One proven method of making a grayscale mask is to use e-beam lithography, where a high-energy-beam-sensitive (HEBS) material is exposed by e-beam, and the attenuating factor of the material is related to the electron dose. However, e-beam lithography is a very slow and expensive process, especially for large size structures, which often makes this approach economically unaffordable.
It would be advantageous if a grayscale mask could be fabricated using conventional thin-film IC deposition/photo/etching/ashing steps.
It would be advantageous if a grayscale mask could be fabricated using patterned layers of thin semi-transparent film as a light attenuating material.